The ability to culture in vitro viable three-dimensional cellular constructs that mimic natural tissue has proven very challenging. One of the most difficult of the many problems faced by researchers is that there are multiple dynamic biochemical interactions that take place between and among cells in vivo, many of which have yet to be fully understood, and yet the complicated in vivo system must be accurately modeled if successful development of engineered tissues in vitro is to be accomplished. The ideal in vitro system should accurately model the mechanical environment as well as the essential cellular interactions found during in vivo development while providing purity of the desired product construct so as to enable utilization of the product, for instance as transplantable tissue. For example, it is commonly desired that the product cells be isolated and free from extraneous cells of other phenotypes, and in particular those previously shown to exhibit unfavorable attributes following implant (e.g., tumor generation or immune system reaction). However, biochemical interaction between those less than desirable cell types with the product cells may be necessary for the healthy growth and development of the product cells, for example due to their introduction of growth stimulation factors into the culture environment.
Many existing co-culture systems are simple well plate designs that are static in nature and do not allow for manipulation of the local environment beyond the gross chemical inputs to the system. As such, the development of more dynamic co-culture systems has become of interest. However, known dynamic systems, similar to the static systems, often provide only a single source of nutrients/growth stimulants/etc. to all of the cell types held in the system. Moreover, the different cell types that are co-cultured in both static and dynamic systems are usually maintained in actual physical contact with one another, preventing the development of an isolated cell population, and also limiting means for better understanding the biochemical communications between the cell types during growth and development.
There are some systems in which an attempt has been made to physically separate cell types in dynamic systems, for instance through location of a porous substrate between the two cell types. However, in these systems, all cell-types cultured in the system are still subjected to the same culture media, similar to the above-described static systems. Additionally, the porous substrate usually also serves as the support scaffold to which cells are intended to attach and grow. Attachment of cells to the porous substrate will alter the flow characteristics of biochemicals across and through the substrate, which in turn affects communication between the cells.
What is needed in the art is a method for co-culturing multiple cell types in a dynamic environment in which the different cell types can communicate biochemically, and yet can be separated physically. Moreover, what is needed is a system in which cells can be developed to form a three-dimensional construct, while maintaining the isolation and purity of the developing product cells and at the same time allowing for biochemical communication between cells of different types.